Heat regulating system



May 12, 1936. R. E, OLSON 2,040,328

HEAT REGULAT ING SYSTEM Filed March 1, 1935 Solehoia Operafea INVENTOR RArMonmE.0Lsozv ATIORN Y 15 from the intake and Patented May 12; 1936 UNITED STATES PATENT OFFICE.

BEAT REGULATING Raymond E. Olson, fiochester N. Y aselgnor. to

Taylor Instrument Companies, a corporation of New York Application March 1,

. 12 Claims. This invention relatesto :heat regulating s"ysterm for drying ovens. a

In certain types of ovens, particularly in lacquer or enameldrying ovens wherein explosive 5 mixtures are generated inthe course of drying processes, it is necessary to provide various safeguards to prevent explo onsresulting from such mixtures.

The main feature of the present invention therefore relates to a novel arrangement for regulating the temperature of a drying oven while aflording .complete security against explosions withintheoven. r OtherLfeatures of the invention will appear detailed description and claims when taken with the single drawing which'diagrammatically illustrates the invention. In this drawing l designatesa drying oven, such as is I used in the drying of enameled articles, which is provided with a stack! for theescape of fumes. This oven is heated by air circulated through the oven but heatedexternally thereof in a heater 3 to which fresh air is supplied through the intake 4 of the heater. Since the circulating, air from the oven contains explosive fumes, it is desirable to heat this airby direct'contact with an exposed flame to consum these fumes as they are gener ated. However, if the air circulation stops for any appreciableinterval, an explosive mixture- 30 from the drying lacquer or enamel will accumulate inthe oven and on contact with the'flame in the heater, will cause an explosion. In order to prevent such 'an explosion it is required that the oven be purged, I 35 must be removed therefrom before the gas flamecan' be ignited and. the regulating system made effective. This purging of the oven is effected since fresh air to. the amount of ten-per cent of.

the volume of the system is introduced at the 40 intake 4, and also since the recirculation is rapid, the entire oven atmosphere being passed through the heater not less than twice per minute andiin some. cases' as often as six times per minute. With ten per centfreslri air introduced at, the consequently ten per cent -of the gasladene'd air exhausted through the stack 2 at each recirculation and if the air is recirculated twice it will be appreciated that the entire atmosphere within the oven will be purged or, cleared ofdangerous' fumes within a predeter-" mined time interval, herein assumed to be eight minutes. i V It is believedthat the various safeguarding features willbest' be understood by describing the 55 operations. involved in s the oven into opper minute,

' throughout the that is, all of the vapors therein Rochester, N. Y.,

1935, Serial No. 3,945

erationand in regulating the temperature thereof, as well as setting forth the various controlling operations which take place whenany abnormal condition arises in the system. It has been mentioned that the oven l is heated by air circulated 5 in piping extending from the outlet of the oven through the pipe 6, through theheating chamber 3, past the flame at the gas jet 8 as well as past the vane 9, and thence through the circulating fan II, which is driven by the motor II, and Ill :through the pipe 2 to the inlet of the oven. Let .it be assumed that the gas pressure in the pipe I! leading to the jet 8 is at a normal predetermined value under which condition the capsular diaphragm or bellows the valve IS' in the compressed air line, but if the gas pressure drops below the predetermined value the valve [5 will close as will hereinafter be described, to shut off the operation of the oven.

In accordance with a further -safeguarding feag0 ture, the fan It in the pipe I! must be operated for a predetermined intervaLsufliciently long to remove all of explosive gases from the oven. For purposes of this invention, it is assumed that the oven can be completely cleared of explosive gas-ina period of eight minutes and this time interval will be referred to by way of example specificatiom -When, therefore, it is desired'to start the oven into operation, the fan III is started and the air supply is introduced into the conduit I6, thereafter the regulating system automatically efiects complete heat regulation within the oven to a desired temperature.

Under thecondition above-named, compressed "air flows thro gh the conduit l6, valve i5, con- "duit H1, and the vane-operated valve l8, and. thence through conduit It to the diaphragm of the motorvalve 20 which controls the exhaust pipe leading from' an air reservoir 2|. Compressed air flowing through the conduit 19 also 40 passes slowly through the constriction li into the reservoir 2| and since the exhaust pipe from this reservoir is now closed, air pressure will slowly build up in the reservoir until this pressure has reached a predetermined value, for example, nine pounds per square inch.-

' Since the fan lll must be in operation preferably for eight minutes before the heating gas can be supplied to the jet Q and ignited, the con- 'striction 22 should be of such size that pressure in the reservoirll will not reach nine pounds per square inch until the 'end of the, eight-minute interval. v

It should be mentioned that the air relay-valve I8 is the 'vane-operatedtypc, that is, when the 3 It will be expanded to open l5 60 layed for a brief interval after the operation of compressed air is the start to measure the 'of the motor valve circulating. air flows past the vane, it moves to' its position shown in dotted lines, wherein the valve I8 will be opened. It will thus be seen that before the reservoir 2I and the constriction 22 prescribed time interval, the vane-operated valveIB must be opened which can only be effected as a result of the operation of the circulating fan I0 to remove explosive fumes from the oven.

When the air pressure in the reservoir 2| reaches a value of nine pounds per square inch,

this pressure will be. applied through the conduit 23 to the. diaphragm top of the motor valve 25. when the motor valve 25 is thus operated, supplied through conduit 30, through the normally closed solenoid valve (now assumed to be open) and through constriction 21, to the diaphragm top of the motor valve 28. The constriction 21 in the conduit is provided to insure that the motor' valve 28 will not operate until a predetermined interval following the operation of the motor valve 25, as will be set forth.

Conduit 30 also supplies compressed airthrough branch conduit 3| to the primary regulating unit'RI and through the branch conduit 32 to the secondary regulating unit R2. The conduit 30 further communicates with the diaphragm top 33in the-branch 34 of the gas line leading to the pilot jet 35 and, in addition, communicates with the electro-pneumatic switch 36, of well-known construction which includes a metal bellows 36a operating-in response to air pressure changes to control switch contacts 366. This switch on closing completes a circuit, including the conductors s1 and 38 connected in series with the primary winding of the transformer 39 and a source of electric current. When the system is in operation, this circuit is periodically interrupted at the conswitch. Thus with the electro-pneumaticswitch 36 closed and the valve 33 opened, to permit gas to flow through the conduit, 34 to the pilot jet 35 on each make and break of the primary circuit of the transformer 39, current will flow from the ground through the secondary winding of the transformer, conductor 44, spark plug 45, to ground. This periodically generates a spark at the spark plug 45toignite the pilot light at jet 35 in the event that it has been extinguished accidently. It has been mentioned that the operation of the motor valve 28 in the gas line is dethe motor valve 25. This insures that the pilot light at ,jet 35 will be burning at the time that the valve 28 opens the gas line leading to the jet 8.

the closure of ,its'

scribed to throttle rises to the predetermined temperature which is herein assumed to be 400 B. As soon as this temperature is reached, the tube system of the primary regulating unit RI takes up the control of the temperature of the oven. This tube system, as is well-known, includes a bulb 48 communicating through a capillary 49 with a Bourdon spring 50, which tube system contains a heat-sensitive medium such as a liquid.

a vapor, or a combination of both. When the temperature in the oven fluctuates, the filling medium in the tube system expands or contracts and thereby causes the Bourdon spring 50 to unwind or to wind up.- The free end of this spring which is connected by a link 5| to a pen arm 52, swings this pen arm about its pivotal mounting 53 on the frame of the unit. This pen arm is provided at its lower end with a stylus 54, which is in operative relation to a graduating chart 55 arranged to be actuated by suitable clock mechanism (not. shown) so that a temperature record in the form of a line is drawn on this chart. The upper end of the pen arm 52 is connected by a link 56 to the upper end of an arm 51 which is pivoted at 58 on the frame so that the movement of the pen arm causes a corresponding movement of the arm 51. The arm 51 is arranged to actuate a baflie 59 pivoted at v60 on the frame of the instrument. The baflle 58, ex-

cept when thus moved away by the arm 51, engages the ends of the nozzle 6|. It will be understood that compressed air flowing through the conduit 3 I, branch conduit 52, constriction '63 and conduit 64, escapes slowlyv through the nozzle GI, except when its escape is impeded by the baiile 58. The branch conduit 64 also communicates with the capsular diaphragm or bellows G5 which controls the operation of a pilot valve 66.

When the temperature in the oven 5 reaches the predetermined value, that is, 400 F., the filling medium in the tube system will actuate the Bourdon spring which through the link 5|, pen arm 52 and link 56, swings the arm 51 clockwise so that the lower end of the baiiie 59 is moved away from the nozzle GI. Air pressure in the branch conduit 64 is thereby reduced, owing to the unimpeded escape of air hrough the nozzle GI, to cause the capsular diaphragm 55 tocontract, thereby permitting compressed air to flow through the branch conduit 6|, conduit 61 to one motor valve 46; This tends to cause the valve 46 to close, reducing the flow of heating gas through pipe I3 to the jet 8.

It will be understood that the regulating instrument RI will operate in the manner just dethe valve 46 so that the proper amount of gas reaches the jet 8 in order to maina value that the oven I is maintained at 400 F.

RI. This unit is also provided with a tube system including a bulb I0 communicating through the capillary tube II with the Bourdon spring 12,

which tube system is likewise filled with a suitable heat-sensitive medium of the same character as that provided in the regulating unit RI. The bulb I0 of the unit R2 is mounted in the pipe I2 in the path of the circulating air and the unit R2 is preferably adjusted so that it win maintain the temperature of the air passing through this pipe at a value slightly higher than that norits ,= amass maliy'maintainedby the the u in the bvehJ-m example, a temperature of 425 1". It will be understood that-therregulating unit RI normally eflects the desired heat regulating within the g oven, but if forany reason this unit tails to maintain the desired temperature, the regulating unit R! will immediately take uprthe heat regulation of oven when temperature reaches 425 l t, and thereby prevent this temperature from rising beyond safe limits. 1

Let it be assumed that the instrument RI fails, to operateso that the ,tem'peraturewithin' the pipe I! rises to 425 F. when this temperature is re ched, including the :bulb I0, expands and thereby causes the Bourdon spring which is connected by link II to the pivoted pen arm 14, swings this pen arm clockwise about its pivot I5. This movement of the pen arm which filo is connected by a link 16 to the upper end of the baiiie actuatingarm l'l, moves the actuating arm about its pivot I 8. Arm 'I'I swings 'the battle ll about its pivot O! in aclockwise direction. I

1 It-will be understood that during the operation of the system, compressed present in the hrauch conduit 32 passes through the constricition iito the branch conduit l2. This conduit communicates with the opening in thenoszle I, but since the baflle I1 normally impedes the escape of air through nozzle, the pressure in thebranch conduit, will be such that the capdiaphragm N is expanded to close the relay valve 85. This permits compressed air to now fromthe branch conduit 32 throughithe 'relay valve ",conduitlt, to the second diaphragm chamber at the top of the motor valye', thereby tending to close this valve." In this manner the unit R2 operates to throttle the motorvalve l! in the gas line, to maintain the flame at the jet [of-such size that the temperature atthe bulb [Iis held at 425 F. e I litv the' gas pressure in the pipe It falls below the predetermined value, valve II will close. Likewise, it the fan ll fails to operate the vane S will swing to its vertical position and thereby close the valve It. On the closure of either of these valves, compressedair will be out off from all the conduit II, with the result that the spring of-the motor valve 10' will immediately open this valve so that the air' in the reservoir 21 is almost immediately exhaustedwhen this takes place,

fair pressure will immediately be removed from diaphragm'top of the motor valve 2 and its spring will immediately close. this valve. This conduit ll, As. a result of the drop in air presin conduit'fl, the motor valves .2. and 33 are immediately operated by their respective w ngs to closejhega pipes leading to the let I and the branch gas pipe 34 leading to the pilot jetl l'. The closing of valve II also'causes the electro-pneumatic tch "to open so that no apart is generated at the spark plug 4!,

8 in thepower circuit supplying current to the ig'niter, is closed before the oven is. started in 2 operation and in order .to stopthe operation of the oven in, the event of electric power failure, the previously mention electrically operated valve Ills provided in the conduit as indicated. This valve is of the typ which is normally closed, that is, itis open only when its solenoid is energised. During while'the switch 8 is closed and while the pneumatic switch I. .is

the filling medium in the tube syste 83 to unwind. This spring.

result in the cutting off of air pressure from the ii In order to ensure thatthe double throw switch the operation of the oven,-

als closed, the solenoid ofvalve ll is energized so that this valve is spell. The energizing circuit for opening the valve, is traceable from one side of the alternating current source, through one blade of the switch 8,

conductor 31, contacts 36b of the switch 36, con- 5: ducto'r-ll, winding of the valve 90, conductor 92 and through the other-blade of the switch S, to the other side of the alternating current source. By this arrangement, if current is not supplied tothe igniter' either due to the fact that the cur-k rentsupply has failed, or to the fact that the operator has neglected to close the switch 8, or

due to a failure of the electro-pneumatic switch 30, the solenoid of the valve 90 will not be energized and thevalve will be closed. This will prevent compressed air flowing through the conduit 30 to the diaphragm topof the motor valve 28 1 in the 'gas' supply line, or to the diaphragm top 4 of the motor valve 33 in the gas pilot line so that both Iof these valves will be closed to cut oil the flow of gas, until the electrical circuit to the igniter-is positively completed.

when normal conditions have been restored so that the oven canagain be put into operation, the fan 1! must be operated for an eight-minute gs interval before the gas let can be ignited. This result is effected in the same manner as when, startin the furnace-originally; in other words, on any is ore of the fan III or low gas pressure, both gas Jets-l and are extinguished immediately, but before these jets can'be relighted it is necessary for interval of at least eight minutes to elapse.- By this arrangement, accurate temperature regulation is effected with complete security against gas explosions.

I claim: d

1. In a system of the class described, an oven, a heater therefor, a pipe supplying gas to said heater for heating said oven, a valve controlling the' flow 0! gas through said pipe, means for igniting the gas at said heater, means for withdrawing a stream of air and fumes from said oven, means for measuri g a predetermined time interval following the initiation of the flow of said stream of air and iumes, said time measuring means init means responsive to the now of said stream oi air and fumes for supplying fluid from said source to said-reservoir through a restricted oriflce,means responsive to a predetermined pressure reservoir for opening the valve in said gas he and for operating said igniting means,-and thermo-responsive means controlling the flow of gas through said pipe whereby the temperature within the oven' is maintained at a predetermined, to

value. v 2. In a system oi the class described, a source A of pressure 'fluid; anoven, a gas pip suppiying'. gas to a flame for heating said oven, a pressure-i cluding-areservoir and a source of pressurefiuid,

fluid operated valve controlling the flowof gas through said pipe, -means for withdrawing a stream of 'air and fumesfrom said oven in con-- tact with said flame. for consuming said fumes, timing means for measuring a predeterminedv time .interval followi'ng the initiation of the flow 35 from said source to said valve foropening the same. I

3. In a system of the class described, a source of pressure fluid, an ove a gas pipe supplying gas to a flame for heating said oven, at pressurefluid operated valve controlling the flow of gas Q3 insaid 50' means, means operated by-said timing means to' .the heat supplied flow of gas through source to said valve through said pipe, stream of air and means for withdrawing a fumes from said oven in contact with said flame for consuming said fumes,

timing means for measuring a predetermined time interval following theinitiation of the flow'of said stream of air and fumes, flow-responsive meansv controlled by said stream for starting said timing control the application of pressure fluid from said for opening the same, and regulating means responsive to to said oven for controlling the said pipe whereby the temoven is maintained at a prethermo-sensitive perature within the determined value.

4. In a system of the classdescribed, a source of pressure fluid, an oven, a gas pipe supplying gas to a' heater for heating said oven, a pressurefluid operated valve controlling the flow of gas through said pipe, means for withdrawing a stream of air and fumes from said oven, timing means for measuring a predetermined time interval following the initiation of. the flow of said stream of air and fumes, means responsive to the said oven, a valve controlling air and fumes, said'measuring means including a reservoir, a second valve controlling the outlet of said reservoir and a source of pressure fluid,

means responsive to the flow of and fumes for-supplying fluid from said source to said reservoir through a restricted orifice and to said second valve to operate the same for closing said outlet, and means responsive to a predeterair and fumes, said .of the valve in said mined pressure in said reservoir for opening said' first-mentioned valve.

6. In a system of the class described, an oven, a gas pipe supplying gas to a heater for. heating said oven, .a first valve controlling the flow of gas. through said pipe, means for withdrawing a stream of air and fumes from said oven, means for measuring a predetermined time interval following the initiation of the flow of the stream of measuring means including a reservoir, a valve controlling the outlet of'said reservoir. and a source of pressure fluid, means responsive to the flow of said stream of air and fumes for supplying fluid from said source to said reservoir through a restricted orifice and to said second valve to\ operate the same for closing said outlet, means responsive to a predeterminedpressure insaid'reservoir for controlling the opening drop in said pressure below said predetermined value for closing said flrst'yalve.

7. In a system of theclass described, a source of pressure 'fluid, an oven, a gas heater for heating said oven, a gas pipe supplying gas to said eater, a regulating valve in said pipe, means for withdrawing a stream of air and fumes from said oven, timing means for measuring a predetermined time interval following the initiation of the flow-of said stream of air and fumes, flow responsive' means controlled .by said stream for ttarting'said timing means-means operatedby means for measuring withdrawing a said stream of air said oven,

gas line and responsive to a said-timing means to control the applicationgoi pressurefluid from said source to said valve for opening the same, including a secondmressure-fluid operated valve insaid pipe controlling the flow of gas there-.

through-whereby the temperature within the oven is maintained at a predetermined value.

8. In a system of the class described, an oven, gas p pe Supp ying gas to a flame for heating said oven, a first valve controlling the flow of gas through said pipe, means for withdrawing a stream of air and fumes from said oven in contact'with said flame for consuming said fumes,

a predetermined time interval following the initiation of the flow of said stream of air and fumes, said measuring means including a reservoir, a. second valve controlling the outlet of said reservoir and a source of pressure fluid, means responsive to theflow of said stream of air and fumes for supplying fluid from said source to said reservoir through a restricted orifice and to said second valve to operate the same for; closing said outlet, means responsive to a predetermined pressure in said reservoir for opening the valve in said gas line, and thermo- "responsive means controlling thev flow of gas and thermo-responsive means through said pipe whereby the temperature within the oven is maintained at a predetermined value. l

9; In a system of the class described, an oven,

11 as pipe Supp ying gasto a flame for heating said oven, a first valve controlling the flow of gas through said pipe, means for withdrawing a stream of air and fumes from said oven in contact with said flame for consuming said fumes,

means for measuring a predetermined time interval following the initiation of the flow of said streamof air and fumes, said measuring means including a reservoir, a second valve controlling the outlet'of said reservoir and a source of pressure fluid, means responsive to the flow of said stream of air and fumes for supplying fluid from said source to said reservoir through a restricted orifice and to said second valve to operate the to a predetermined pressure in said reservoir for opening the valve in said gas line, primary thermo-responsive means controlling the flow of gas through said pipe whereby the temperature within the oven mined value, and secondary thermo-responsive. means controlling the flow of gas through said pipe and set into operation by the failure of said primary thermo-responsive .means whereby the temperature within said oven is'maintained at apredetermined value. s

10. In' a, system of the class described, an oven, a gas P p pplying gas to a flame for heating a first valve controlling the fiow of gas through said pipe, means for withdrawing a stream of air and fumes from said oven in con-.

to said reservoir through a restricted orifice and to said second valve to operate the same for closing said outlet, and means responsiveto a predetermined pressurein said reservoir for opening the valve in said gas line.

is maintained at a predetersame for closing said outlet, means responsive 11'. In a system of the class described, a source of pressure fluid, an oven. a gas-pipe gas to a flame film-heating said oven, a pressurefluid operated valve controlling the flow of gas through said pipe, means for withdrawing a stream of air and fumes from said oven in contact with said flame for consuming said fumes, timing means for measuring a predetermined time interval-following the initiation'of the flow timing means,

of said stream of air and fumes, flow-responsive means controlled by saidstream for starting said means operated by said timing means to control the application of pressure fluid from said source to said valve for opening, the same, a source .of electric current, and means including 'said current source for periodically applying an igniting sparkto said gas.

12. In a system of the class described, a source of pressure fluid, an oven, a gas pipe supplying gas to a flame for heating said oven, apressurefluid operated valve controlling the flow of gas through mid pipe. means for withdrawing a stream of air and fumes from-said oven in contact with said flame for consuming said fumes, timing means for measuring a predetermined time interval following the initiation of the flow of said stream of air and fumes. flow-responsive means controlled by said stream for starting said timing means, means operated. by said timing means to control the application of pressure fluid from said source to said valve for opening the same, a source of electric current, means including said current sauce for periodically applying an igniting spark to said gas, and means responsive to the failure of said current for closing said valve. v

RAYMOND E. qrsou. 

